The use of conventional heparin in pregnancy has been associated with significant maternal morbidity as a result of heparin induced adverse effects on bone density resulting in clinical, subclinical and occasional bone fracture. The emerging new fractionated heparing in its low molecular weight form may have less adverse effects on bone density, this has been proven in animal data, while the available human data are scarce and conflicting. This study may shed some light on this very important complication of heparin therapy during pregnancy.